The present invention relates to mechanical face seals and in particular to mechanical face seals in which one seal face member is secured in fixed rotational relationship and sealed with respect to one of a pair of relatively rotatable components so that it is movable axially with respect thereto, by means of a resilient bellows unit.
With seals of this type, when the bellows unit fails due to fatigue, this normally occurs at the convolution adjacent the end by which it is rigidly secured to the associated component. Stressing of the bellows unit results from three effects:
a) axial compression of the bellows unit by means of which an axial load is applied to the seal face member urging it into sealing engagement with a second seal face member associated with the other component; PA1 b) loading due to the pressure differential across the bellows unit; and PA1 c) vibrational loading.
The end of the bellows unit which is rigidly secured to the associated component, must support the rest of the bellows unit and is not flexibly mounted in the same way as the other convolutions and will consequently be more highly stressed, particularly with regard to vibrational loading. Stressing of the other end of the bellows unit, which is attached to the seal face member or a carrier ring for the seal face member, could also be above average.
The present invention provides a bellows unit in which stresses are more evenly distributed.